1. Field of the Invention
The present invention relates to a friction pad of a disc brake which is mounted on a vehicle, such as an automobile or a motorcycle.
2. Description of the Related Art
In a disc brake for controlling the action of a brake disc by a pair of friction pads, the brake disc is made of cast iron or a steel plate and the friction pads are made of a resin mold. Improvement in durability of the brake disc and the friction pads to a heat crack and fade, and their lightening in weight have been desired.
As disclosed in Japanese Unexamined Patent Publication No. 1-320328, for example, a carbon-carbon composite or a carbon-fiber reinforced carbon composite has been proposed as the materials for the brake disc and the friction pads.
Carbon fibers impregnated with a carbon matrix are subjected to carbonization and high densification treatment to provide the carbon-carbon composite. This composite has a great friction coefficient when combined with the same type of a material, and a small friction coefficient in a combination with a different type of a material. The carbon-carbon composite is therefore used for both the brake disc and the friction pads.
The carbon-carbon composite has a large friction coefficient in a high temperature range of about 100.degree. C. or higher, and has excellent heat resistance, thermal shock resistances, and heat conductivity. This composite however has a great wear by oxidation rate in such a high temperature range, so as to deteriorate the durability of the friction pads and easily transmit heat caused by a braking operation to a hydraulic system.
Further, since the carbon-carbon composite is hardly bonded or fusion-bonded to other materials, the entire friction pad is integrally formed of the carbon-carbon composite as disclosed in the Japanese publication (No. 1-320328). This type of friction pad is inferior in rigidity to those provided with metal back plates, and will therefore be deformed by the pressure of a piston, or impart a soft brake feeling to a driver. Also as the carbon-carbon composite has high heat conductivity, an excellent insulator has to be attached to the back surface of the friction pad as a countermeasure for vapor-lock.
In this respect, it has been proposed to provide a friction pad which has a back plate of a different material coupled to a carbon-carbon composite lining by rivets or the like. Since a plurality of heavy rivets are used for this friction pad, the total weight of the pad increases even with the use of the carbon-carbon composite.